netdev - Re: [PATCH net] flow_dissector: disable preemption around BPF calls

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Message-ID: <CANn89iJzsUbLXB_M5UZr2ieNyQdGHsKPFzqeQFGtKtL8d9pu0Q@mail.gmail.com>
Date:   Mon, 13 May 2019 10:20:19 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        bpf <bpf@...r.kernel.org>, syzbot <syzkaller@...glegroups.com>,
        Petar Penkov <ppenkov@...gle.com>,
        Stanislav Fomichev <sdf@...gle.com>
Subject: Re: [PATCH net] flow_dissector: disable preemption around BPF calls

On Mon, May 13, 2019 at 10:17 AM Mark Rutland <mark.rutland@....com> wrote:
>
> On Mon, May 13, 2019 at 09:38:55AM -0700, 'Eric Dumazet' via syzkaller wrote:
> > Various things in eBPF really require us to disable preemption
> > before running an eBPF program.
>
> Is that true for all eBPF uses? I note that we don't disable preemption
> in the lib/test_bpf.c module, for example.
>
> If it's a general requirement, perhaps it's worth an assertion within
> BPF_PROG_RUN()?


The assertion is already there :)

This is how syzbot triggered the report.